The present invention relates to electrical primers and ignitors, and more particularly to an RF-insensitive semiconductor slapper-type ignitor for use in firing in-line low order explosives rapidly and reliably.
Conventional explosives employ mechanical or electrically initiated charge ignitors to create an ignition train which sets off the main propellant. Mechanical propelling charge ignitors are usually provided with percussion caps which are made to fire upon exposure to a mechanical impulse such as that caused by a firing pin or hammer blow. Electrically initiated charge ignitors, on the other hand, fire under the influence of a current pulse which may melt a resistive bridge wire, vaporize a metallic layer at an arc point, or pass through an electrically conductive charge.
Presently, in-line low order explosives are fired by applying a high voltage across a bridge wire which in turn breaks down, thereby propelling a plastic disc (typically around 0.005 inch in diameter and 0.001 inch thick) into the primary charge. U.S. Pat. No. 4,840,122 is an example of such a device.
A problem with bridge wire slapper devices is their sensitivity to electromagnetic (EM) radiation. EM fields may couple with the bridge wire ignitor causing premature initiation. This problem is particularly acute aboard naval vessels which typically support multiple high power electromagnetic sources in close proximity to ordnance.
Various solutions to the problem of EM susceptibility in electrical ignitors, and to RF fields in particular, are discussed in U.S. Pat. No. 5,085,146 to Baginski, and copending U.S. patent application, Ser. No. 866,776, both of which are hereby incorporated by reference. Both devices employ a semiconductor in which two p-n junctions have been created on top and bottom surfaces of a silicon substrate. Conductive layers atop the p-n junctions channel the firing current through the junctions, causing a small plug of conductive material on the top surface to vaporize, thereby igniting an electrically conductive primer charge. These devices, however, function only with high order explosives, relying on contact with a conductive primer mix. They will not fire ammunition currently fitted with slapper-type ignitors, which employ low order explosives and require the slapper ignitor for reasons of safety.